Commit 5dee99b2 authored by James Hogan's avatar James Hogan
Browse files

KVM: MIPS/Emulate: Update CP0_Compare emulation for VZ 



Update emulation of guest writes to CP0_Compare for VZ. There are two
main differences compared to trap & emulate:

 - Writing to CP0_Compare in the VZ hardware guest context acks any
   pending timer, clearing CP0_Cause.TI. If we don't want an ack to take
   place we must carefully restore the TI bit if it was previously set.

 - Even with guest timer access disabled in CP0_GuestCtl0.GT, if the
   guest CP0_Count reaches the guest CP0_Compare the timer interrupt
   will assert. To prevent this we must set CP0_GTOffset to move the
   guest CP0_Count out of the way of the new guest CP0_Compare, either
   before or after depending on whether it is a forwards or backwards
   change.

Signed-off-by: default avatarJames Hogan <james.hogan@imgtec.com>
Cc: Paolo Bonzini <pbonzini@redhat.com>
Cc: "Radim Krčmář" <rkrcmar@redhat.com>
Cc: Ralf Baechle <ralf@linux-mips.org>
Cc: linux-mips@linux-mips.org
Cc: kvm@vger.kernel.org
parent 372582a6

arch/mips/kvm/emulate.c

+42 −1
Original line number Diff line number Diff line
@@ -621,7 +621,9 @@ void kvm_mips_write_compare(struct kvm_vcpu *vcpu, u32 compare, bool ack) 
	struct mips_coproc *cop0 = vcpu->arch.cop0;

	int dc;

	u32 old_compare = kvm_read_c0_guest_compare(cop0);

	ktime_t now;

	s32 delta = compare - old_compare;

	u32 cause;

	ktime_t now = ktime_set(0, 0); /* silence bogus GCC warning */

	u32 count;



	/* if unchanged, must just be an ack */
@@ -633,6 +635,21 @@ void kvm_mips_write_compare(struct kvm_vcpu *vcpu, u32 compare, bool ack) 
		return;

	}



	/*

	 * If guest CP0_Compare moves forward, CP0_GTOffset should be adjusted

	 * too to prevent guest CP0_Count hitting guest CP0_Compare.

	 *

	 * The new GTOffset corresponds to the new value of CP0_Compare, and is

	 * set prior to it being written into the guest context. We disable

	 * preemption until the new value is written to prevent restore of a

	 * GTOffset corresponding to the old CP0_Compare value.

	 */

	if (IS_ENABLED(CONFIG_KVM_MIPS_VZ) && delta > 0) {

		preempt_disable();

		write_c0_gtoffset(compare - read_c0_count());

		back_to_back_c0_hazard();

	}



	/* freeze_hrtimer() takes care of timer interrupts <= count */

	dc = kvm_mips_count_disabled(vcpu);

	if (!dc)
@@ -640,12 +657,36 @@ void kvm_mips_write_compare(struct kvm_vcpu *vcpu, u32 compare, bool ack) 


	if (ack)

		kvm_mips_callbacks->dequeue_timer_int(vcpu);

	else if (IS_ENABLED(CONFIG_KVM_MIPS_VZ))

		/*

		 * With VZ, writing CP0_Compare acks (clears) CP0_Cause.TI, so

		 * preserve guest CP0_Cause.TI if we don't want to ack it.

		 */

		cause = kvm_read_c0_guest_cause(cop0);



	kvm_write_c0_guest_compare(cop0, compare);



	if (IS_ENABLED(CONFIG_KVM_MIPS_VZ)) {

		if (delta > 0)

			preempt_enable();



		back_to_back_c0_hazard();



		if (!ack && cause & CAUSEF_TI)

			kvm_write_c0_guest_cause(cop0, cause);

	}



	/* resume_hrtimer() takes care of timer interrupts > count */

	if (!dc)

		kvm_mips_resume_hrtimer(vcpu, now, count);



	/*

	 * If guest CP0_Compare is moving backward, we delay CP0_GTOffset change

	 * until after the new CP0_Compare is written, otherwise new guest

	 * CP0_Count could hit new guest CP0_Compare.

	 */

	if (IS_ENABLED(CONFIG_KVM_MIPS_VZ) && delta <= 0)

		write_c0_gtoffset(compare - read_c0_count());

}



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